In a mobile communication system, a handover is performed when a mobile device moves from a communication area of a certain wireless base station in which the mobile device is currently in communication to a communication area of another wireless base station. Various handover technologies have been proposed.
For example, Non-patent Document 1 discloses a technology related to a handover method in which a base station controller controls each wireless base station without direct transmission of signaling information or user data between wireless base stations in a mobile communication system that connects a plurality of wireless base stations to which a mobile device is connected to the base station controller with wired lines.
Specifically, the mobile device measures communication quality of a wireless line connected to a wireless base station that the mobile device is not currently communicating with. If the measured communication quality is higher than that of a wireless line connected to the wireless base station that the mobile device is currently communicating with, the mobile device sends the measured result to the base station controller.
The base station controller establishes a wired link between the wireless base station with the good result and the base station controller, and instructs the wireless base station to which the wired link has been established (a destination wireless base station) to establish a wireless link to the mobile device. After the destination wireless base station completes establishment of the wired link to the base station controller and preparation for establishment of the wireless link to the mobile device, the base station controller instructs the mobile device to establish the wireless link to the destination wireless base station via the wireless base station that the mobile device is currently communicating with.
After switching (handing over) the wireless line from the wireless base station that the mobile device is currently communicating with to the destination wireless base station, the mobile device notifies the base station controller via the destination wireless base station that the handover has been completed.
However, the handover method described in the Non-patent Document 1 involves a problem that the handover takes a long time due to a heavy processing load on the base station controller at the time of the handover because a wired line between the destination wireless base station and the base station controller is switched every time a handover of a mobile device occurs.
To solve the problem, according to the conventional technology described in Patent Document 1, a single master base station connected to public switched telephone networks (PSTN) and a plurality of slave base stations are serially connected with wired lines, and the master wireless base station comprehensively controls the slave wireless base stations. In this manner, the master wireless base station establishes the wired links among the wireless base stations and manages a location of the mobile device so that the handover is performed at a high speed.
Patent Document 1: Japanese Patent Laid-open No. H10-271553
Non-patent Document 1: 3GPP TR25.931 V5.1.0 (2002-06)